In most applications where a rotary shaft is suspended by means of an active magnetic suspension servo-controlled on the basis of sensors for detecting the position of the rotary shaft, auxiliary bearings, also known as emergency bearings, and generally in the form of ball bearings or roller bearings are provided in order to support the shaft while the machine is being stopped or in the event of a failure of the magnetic suspension, thereby preventing direct contact between the magnetic circuits of the rotors and the stators of the magnetic bearings when the windings of the stator electromagnets are no longer powered, thus avoiding damage to the laminations thereof. In normal operation, auxiliary bearings leave clearance about the rotary shaft and do not themselves rotate. The clearance provided for the auxiliary bearings is generally about one half the width of the air gap of the magnetic bearings.
Conventional emergency bearings used in the event of failure in the magnetic suspension may be mounted either on the rotary shaft while leaving clearance between the outer ring of the bearings and the stator, or else on the frame while leaving clearance between the inner ring of the bearings and the rotor. In either case, whenever a rotating portion lands on the fixed portion of the bearing, motion is not always stable and very high stresses may be applied to the cages or rolling components of the emergency bearings which are consequently often damaged. As a result, emergency bearings need frequent replacement and this increases maintenance costs.
The present invention seeks to remedy the above-mentioned drawbacks and to provide an auxiliary bearing for a rotary shaft mounted on magnetic bearings making it possible in the event of the magnetic suspension failing or stopping to receive the rotary shaft without inducing significant disturbance to the motion of the shaft during landing and without the auxiliary bearing being subjected to rapid wear or destruction.
The invention also seeks to provide an auxiliary bearing whose structure is simple and which is easy to mount.